1. Field of the Invention
The present invention relates generally to the field of gas strut technology and more particularly, to gas struts usable for providing a separating force between two stages of a staged rocket apparatus.
2. Description of the Prior Art
FIGS. 22 and 23 schematically illustrate two prior art systems utilizing gas struts to provide a separating force between stages of a staged rocket.
The system in FIG. 22 is a schematic representation of a prior art tank-based gas strut system The system of FIG. 22 relies on a tank containing gas and a distribution system to an array of gas struts. This system is used to produce the separation force for the Delta IV rocket. In this system, 16 short stroke struts push the stages apart. Two tanks are used with ordinance initiated valves to fill the struts through a distribution system. The tanks are very high pressure to reduce their size and make the gas flow fast trough the distributions system. Half of the struts are filled from one tank and the other half are filled by the other tank. The two systems in parallel provide assured separation because there are two independent separate systems onboard. It has the drawback that two systems, each capable of providing the separation force, must be present on the vehicle. This adds weight and cost. The struts have solid rods and have little ability to stabilize the separation by counteracting disturbance forces acting during separation. The Falcon 9 separation struts are similar to the Delta IV struts except there are only 3 struts and the tank is used for other systems as well as the struts. To gain separation reliability, the Falcon 9 system seeks to minimize failure points where the Delta IV system seeks to provide redundancy.
FIG. 23 is a schematic illustration of a prior art gas generator based strut system. This system uses independent gas struts with a gas generator attached to each strut. This system has the advantage that a failure in one part of the system cannot propagate to another part of the system. It has the disadvantage that gas generators burn at a constant rate meaning that the gas generator will not be able to keep up with needed gas at the end of the strut stroke. The initial force will be very high causing a sudden acceleration to the vehicle which is undesirable for tanked liquid propellants. Elaborate profiled grain designs can mitigate this effect to some extent. Mitigation can also be done by over sizing the gas generators and providing pressure relief for the initial part of the stroke. A gas generator strut arrangement was used on X43. In this system, 3 struts were used to drive the Pegasus booster back from the X43.
Along with gas strut systems such as those of FIGS. 22 and 23, systems based on booster deceleration motors (BDM's) have also been utilized in the past for stage separation to push the stages apart.